Doomsday machine

A doomsday machine was, according to James T. Kirk, "a weapon built primarily as a bluff. It's never meant to be used. So strong, it could destroy both sides in a war."

At the time of the discovery of an extragalactic "planet killer" in 2267, Kirk theorized that the robot weapon was, in fact, that: "a doomsday machine that somebody used in a war uncounted years ago. They don't exist anymore, but the machine is still destroying."

Following the destruction of the "planet killer", Kirk noted the irony of its destruction, stating: "Way back in the 20th century, the H-bomb was the ultimate weapon, their doomsday machine, and we used something like it to destroy another doomsday machine. Probably the first time such a weapon has ever been used for constructive purposes." (TOS: "The Doomsday Machine")